thing is most of the code to make a doom3 game is already open sourced.
i just like wf in fusion. i dunno why, probably because i got my hands on the engine, any borkage and i know why right away. running an engine in the debugger is an experience that i can't explain, but it saves sooo much time.
i also learned allot about why q3 mods have issues with things, and all the "bugs" that existed weren't bugs, they were actually programatic misconceptions about certain fundamentals.